1. Field of the Invention
This invention relates to automatic faucets and particularly to improved temperature control of the water flow from such faucets.
2. State of the Art
Automatic faucets, in which the water flow is started and stopped according to the presence of a user's hands near the faucet, are known. Examples include the following U.S. Pat. Nos. 5,074,520, 5,062,164, and 4,886,207 to Lee et al., U.S. Pat. No. 5,309,940 to Delabie et al., U.S. Pat. No. 4,682,628 to Hill, U.S. Pat. No. 5,095,941 to Betz, U.S. Pat. No. 4,928,732 to Hu, U.S. Pat. No. 5,050,641 to Shwu-Fen, U.S. Pat. No. 4,688,277 to Kakinoki et at., U.S. Pat. No. 4,767,922 to Stauffer, U.S. Pat. No. 3,480,787 to Johansen, and U.S. Pat. No. 3,576,277 to Blackmon. Additionally, UK patent publications Nos. 2 226 105 A by Wu, 2 226 104 A by Wu, and 2 255 625 A by Bosch, and European patent publication No. 0 387 471 A2 by Nilsson and Maattanen also disclose automatic faucets.
However, most prior art automatic faucets have disadvantages. In some cases, installation of the faucet requires construction of additional plumbing and/or electrical lines, making retrofitting of conventional faucets expensive and tedious. In other cases, the temperature of the water from the faucet is not satisfactorily regulated.
First, the water standing in a hot water line prior to the faucet being turned on will typically be cooler in temperature than the hot water supply. Thus, if the desired outlet water temperature is warm or hot, a higher proportion of flow from the hot water valve is needed to produce outlet water of the desired set temperature when the faucet is first turned on. In a conventional manually operated faucet, the user compensates by first opening the hot water all the way, and then as the temperature of the outlet water rises, reducing the hot water flow and opening the cold water valve. However, in a faucet which is activated by a touchless switch, the user cannot, or does not wish, to manually adjust the flows of hot and cold water.
In many automatic faucets, the relative flows of hot and cold water are fixed over the period of activation. That is, when the faucet is turned on, the hot and cold valves open to respective positions computed to provide water of the set temperature assuming that the hot water is at the temperature of the hot supply. Thus, the water which initially leaves the outlet is usually colder than the set temperature. Especially in winter, or if the plumbing is proximal to air-conditioning or refrigeration units, this temperature can be unpleasantly cold. If the period of use is brief, the water at the outlet may never reach the set temperature. If the user tries to wait for hotter water to arrive, water is wasted. In many areas of the country water conservation is a high priority. Or, if the user removes his hands from the faucet area while waiting for warmer water to arrive, the flow of water may be turned off by the automatic sensor.
Further, most such faucets have temperature sensors only in the mixing area downstream of both the cold and hot inputs. A sensor so located will sense a cool or cold temperature when the water flow is activated, and typically the faucet will respond by increasing the proportion of hot water coming to the mixing area. This can result in an overshoot in temperature of the water delivered from the spout, to a temperature that is painfully hot and even scalding. Again responding only to the temperature of the mixing area, the faucet may overcompensate downward, delivering water that is cooler than the set or desired temperature. Thus, the temperature of the water at the output of the faucet may fluctuate initially between too hot and too cold, before finally achieving the set output temperature.
Accordingly, a need remains for an automatic mixing faucet apparatus which delivers water at a uniform preset temperature throughout the period of activation, without large over- or under-shoots and which follows changes in the temperature of water in the hot water line immediately upstream of the mixing area. A need also remains for a temperature regulating system for an automatic faucet, which compensates for the lag time of arrival of hot water. It is desirable that the automatic faucet apparatus and the temperature regulating system should be easily retrofitted to a conventional faucet.